using是什么意思?
using( SqlConnection conn = new SqlConnection( ConfigurationSettings.AppSettings["ConnectionString"] ) )
{
SqlDataAdapter dataAdapter = new SqlDataAdapter( SQL_SELECT_PORTAL, conn );
DataSet dataSet = new DataSet();
dataAdapter.Fill( dataSet );
dropDownList.DataSource = dataSet;
dropDownList.DataTextField = "portalName";
dropDownList.DataValueField = "portalId";
dropDownList.DataBind();
}
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using(){} 这样代表什么意思呀?